Novel Precision Probe Array for Wafer Level Final Test of WLCSP Jathan Edwards

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1 Novel Precision Probe Array for Wafer Level Final Test of WLCSP Johnstech International

2 Presentation Outline Introduction to IQtouch Micro Final Test Probe Arrays for micron pitch WLCSP Compare/contrast with existing technology Probe Array and Probing characteristics Performance data examples Summary and Acknowledgements 2

3 IQtouch Micro Background Johnstech International well established in final package test IQtouch Micro is initial offering into WLCSP final test. 300, 350, 400 and 500 micron pitch available 3

4 IQtouch Micro General Product Scope Ball Count: < 144 Balls / site Package Size: < 10 X 10mm Ball Material: SAC 405, 305, 105, 266, SnAg Ball Diameter: mm (400/500), mm (300/350) Site configurations: Up to 32x and up to 50mm total span Spec Sheet and application notes posted at 4

5 IQtouch Micro Product Configuration Site replaceable elastomeric cartridges for quicker MTTR The elastomeric web is designed to provide controlled probe force to DUT and between two rigid probes Sharp probe tip knife edges for high piercing stress are keyed at 45o to array axis Probe alignment teaching centered to focus in valley 5

6 IQtouch Micro Comparison Performance Vertical Probes Spring Pins Membrane Probes IQtouch Micro Inductance 2 nh 1nH 0.2nH.3nH Bandwidth 1.3 GHz 8 GHz 5 70GHz GHz CRES 1 Ω mΩ mΩ < 50mΩ Cleaning Interval [TD] 100 1, , ,000 3, ,000 Cont. Current (20 o C) 500mA 1.5A < 500 ma 2A Free height [mm] ~ 6mm 3.3mm ~6mm [pedestal] 1.9mm 6

7 Measured RF Characteristics1 SPICE models are fitted to measured data to generate equivalent circuit parameters (e.g. 400 micron pitch): Inductance: Capacitance: nh Self nh Mutual pf Ground pf Mutual 7

8 Measured Digital Signal Characteristics (33 GHz, 10 ps Edge Rate PRBS 2^7-1 Signal) Input Signal Transmitted Signal through Probe pairs and sample / DUT. 8

9 Probe Array Precision X,Y,Z X/Y probe position scatter plot Probe Z-height histogram Standard automated checkout of each probe array via ITC Probilt 3500 Probe Card Analyzer; automated probe capture camera isn t quite as precise as prober, but provides quick validation for each probe s XY Err, planarity, Cres and Force prior to shipment. 9

10 Probing FDR Characteristics Good Cres range (< 100 m ) for ~ 175 microns on SAC ball materials Recommended starting OD at 125 microns 195 microns max (cartridge limit) 10

11 Probing Characteristics: Sample Off Apex Ball Marks OD: 50um 75um 100um 125um 150 um 175 um 5 gpp 7.5 gpp 12 gpp 15 gpp 20 gpp 25 gpp 11

12 Method to Measure Cres directly from Customer Wafers Customers supplied wafers for 300 & 400 micron pitch. We used the common bussed device grounds of the devices to make Cres measurements through I/O pairs. 300 um pitch device; 3 wafer passes with no cleaning required (SAC 305) 400 um pitch device; 7 wafers reprobed few times each; no cleaning required to 200K (SAC 405). 12

13 Customer Performance Data Sample 13

14 Cleaning Interval effect on OEE Cleaning intervals typically depend on WLCSP ball material and the sensitivity of the customer tests (Cpk within test parameter limits). Beta Phase evaluations were drop-in comparisons against competing probe array technologies (VPC and Pogo) where the customer cleaning intervals were often set for touchdowns. In some cases, customers time studies show that up to 10% of total wafer test time is devoted to cleaning stops (i.e. 4 minutes of cleaning and 40 minutes of actual device testing). In one case, we were able to demonstrate extending cleaning interval from 10X per wafer to once per 10 wafers to provide significant Overall Equipment Efficiency (OEE) improvement of the test cell. 14

15 Technical Challenges The higher performance probes require shorter free height than what docking hardware has been designed for in some cases. Usually, this has been accommodated simply with changing prober software z- height limit. In some cases, we have had to supply interposer to increase height to bring probe operating range into prober acceptance range. For drop-in replacement applications, the lower impedance and higher frequency response for IQtouch Micro sometimes require retuning of test programs and/or probe card matching components to be compatible for functional tests. Probe tip recognition for IQtouch Micro in TEL/ TSK prober systems works robustly with some algorithms but not all of them; we are compiling list for recommendations from customer experience. 15

16 Summary and Acknowledgements A brief introduction of the novel precise probe array technology we call IQtouch Micro. This new probe array has the potential to enable new devices types to be final tested at wafer level package. RF performance to enable applications in 5-40 GHz Lower and more stable Cres for improved Cpk and Enhanced cleaning intervals in production environments for improved OEE Thanks to my colleagues at Johnstech with special recognition to: Brian Halvorson, Charles Marks, Jeff Sherry, and Ron Gelbmann (1) Effects of device configuration, Jeff Sherry (Johnstech), Chip Scale Review, May/June 2014 gives a more thorough comparisons of differing ground configurations. jdedwards@johnstech.com 16